Peritonitis is a very common bacterial disease in all avian species leading to economic losses mainly due to mortality and loss of egg production.
Most common bacteria found is E.Coli. Several subtypes of this bacterium are found of which some cause more problems than others, but there is no specific subtype involved.

The underlying reasons for the occurence of this infection are several, but can be categorized on the port of entry of the bacterium into the body.
These ports are:
- The respiratory tract
- The digestive tract
- The reproduction tract
In all these ports, it is normal that a number of bacteria enter the body/bloodstream. Only in case of excessive invasion or serious immunosuppression, that an inflammation of the abdominal cavity will be the result. So the excessive entry of agents is doing the job.

Peritonitis in breeders

In breeders the condition is mainly seen at onset of production until 30 weeks of age. The entry port is mainly the reproduction tract. Bacteria ascend from the cloaca to the infundibulum and in such a way infect the peritoneal cavity. Complicating factor here is that some birds in the flock are overstimulated at start of the production. This results in some yolks being deposited in the peritoneal cavity instead on the infundibulum. In the peritoneal cavity, the yolk is a perfect energy source for bacteria and -importantly - these yolks can not be protected by the immune system since there is no blood circulation.

Some infectious agents and stress can cause also an anti-peristaltic movement in the reproductive tract and deposited yolks are thrown back into the abdominal cavity. Infectious bronchitis is the most known one that can cause this.

Peritonitis in layers (table-egg production)

Next to the system described in breeders, the digestive tract is another important point of entry. To an extent, bacteria leak through the intestinal wall which must be considered as normal. However, in case of enteritis, this leakage is higher and the immune system fails. Constant feed quality is the crucial factor here to minimize the chance for enteritis.

Peritonitis in broilers

In broilers the most important way of entrance is through the respiratory tract. And due to the way of breathing, the air sacs get first inflamed. Air sacculitis followed by pericarditis, perihepatitis and peritonitis. The underlying cause is again a too high entry of bacteria in the air sacs due to inappropriate air filtering in the nostrils and trachea. This filter function by the "hairbrush-cilia" is easily damaged by all kind of viral infections such as infectious bronchitis and newcastle.

The ORT complex (cheese chickens) caused by ornitobacterium rhinotracheale is considered as a separate complex and is described in another info.